Presently, there are two basic methods for along-the-cable underwater profile measurement:
A first method is that the mobile observation platform ascends or descends under the water through controlling the buoyancy and gravity of the observation platform. The method has been applied in most of the basic schemes for the current formed equipment, for instance, a mobile sealed compartment is connected with an outer oil sac which is connected with an inner oil sac via a solenoid valve and an oil pump is pressurized by an electronic circuit controlled air pump in the compartment to discharge the oil from the inner oil sac to the outer oil sac so as to increase the volume of the drain water from the platform, thus increasing the buoyancy of the platform to make the platform ascend. On the contrary, when the oil returns from the outer oil sac to the inner oil sac owing to water pressure, the platform will descend owing to the decrease of the buoyancy of the platform. Although the method can easily control, through its circuit, the slight buoyancy of the platform and change the buoyancy without additional electric power consumption during platform motion, it has the following challenges:    1. The mechanical control part in the compartment is complex and requires a precision air pump, oil pump, solenoid valve and accurate measurements with related sensors;    2. All power is sourced from batteries which have a huge influence on the gravity of the sealed compartment, the design of compartment body is closely related to the quantity of batteries, their service life directly determines the overall design, that is, the battery may affect the whole method;    3. The method, with limited working water depth, is mostly applied to the measurements for the water depth less than or within 2000 m at present, and for the water depth more than 2000 m, the power consumption of the batteries required for pumping the oil to the outer oil sac because the increase of water depth cannot keep balance with the battery efficiency, the overall design of the compartment cannot satisfy further power consumption, thus resulting in failure to complete further measurements.
A second method is that a motor is adopted to drive the gear to climb along the cable. The method works as follows: The moving platform is seized onto the underwater cable via a roller, the platform buoyancy is set zero, the motion of the platform along the cable is driven by the motor in the electronic compartment, the motor drives the gear to rotate, thus driving the roller outside the compartment to move up and down along the cable and the ascending and descending of the platform are controlled through controlling the rotation direction of the motor. The method has the advantages including simple mechanical design part, minor influence of the water depth and simplicity in electronic control but has several difficulties:    1. Every step of platform motion will consume electricity, which constitute a huge challenge to the batteries, and like the first method, there are corresponding requirements on the design of the electronic compartment, the times of the working profiling determines the quantity of the batteries, thus determining the design size of the electronics compartment.    2. The platform, with limited motion speed, requires the motor for every meter of motion in the process of ascending and descending, and huge electricity consumption is required with the increase of the platform motion speed, which constitute a huge challenge to the reliability of the inner motor and outer roller.
It can be seen that the power energy storage mechanism (battery and motor) and measurement mechanism are provided on one platform for the above-mentioned two measurement methods so that there is a problem that the energy for controlling the platform motion is restricted by the battery, thus exerting a decisive influence on the overall design.